Nozzle

ABSTRACT

A nozzle ( 1 ) for use in coating a web-like material by means of high-pressure spraying techniques is manufactured by forming a piece having a tapered duct ending in a closed tip, with a transverse V-shaped groove ( 3 ) subsequently machined in the tip. The angle of the V-shaped groove ( 3 ) is in the range from 25 to 50°, such as 35 to 45°.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national stage application of internationalapp. No. PCT/FI2003/000702, filed Sep. 26, 2003, and claims priority onFinnish App. No. 20021719, filed Sep. 26, 2002.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to the coating of a moving web-like material usinghigh-pressure techniques and it concerns the nozzle used in suchcoating. The invention can be used especially in paper coating.

In paper coating, a coating composition is applied to the paper surfacewith a special view to enhancing the printing characteristics of paper.Conventionally, presses, knife applicators and film-transfer deviceshave been used for coating. These techniques are difficult to implementreliably, especially when an increase in the running speed or coating ofvery thin paper is required.

Spray coating has appeared as the most recent coating technique. It hasthe special advantage of not requiring any mechanical coating means,such as an abrasive knife or rotating rod, in contact with the web.High-pressure spray techniques have proved particularly promising. Herethe coating composition alone, without any gaseous medium, is drivenunder high pressure through a nozzle with small orifices, thecomposition being diffused (atomized) into small droplets. The pressuremay be e.g. in the range from 1 to 200 MPa and the nozzle orifice areae.g. in the range from 0.02 to 0.5 mm². A typical maximum droplet sizeis approximately 100 μm. Such an apparatus comprises a nozzle arrayhaving one or more nozzle rows transverse to the path and consisting ofa plurality of nozzles. The nozzles are disposed so as to cover the webas evenly as possible with the jets. Then jets formed by adjacentnozzles in a nozzle row overlap appropriately at their edges. The jetshape provided by the nozzle depends on the shape of the nozzle orifice.The usual aim is a fan-shaped jet, which is larger in the transversedirection than in the longitudinal direction of the web. Then the nozzleorifice is accordingly oval. To achieve regular coating, the fans arepreferably disposed obliquely to the direction of travel of the web.

Spray coating of paper is described e.g. in the papers FI-B-108061(corresponding to WO 9713036) and Nissinen V, OptiSpray, the New LowImpact Paper Coating Technology, OptiSpray Coating and SizingConference, Finland, Mar. 15, 2001.

Nozzles can be manufactured by making a piece of a suitable material,e.g. a highly wear-resistant material, the piece having a tapered ductending in a closed tip, the desired nozzle orifice being subsequentlymachined in the tip. An oval orifice is provided if a transverseV-shaped groove is machined in the tip. The nozzle material may be e.g.a highly wear-resistant tungsten carbide composition (such as WC+Co).

SUMMARY OF THE INVENTION

The nozzle of this invention is for use in the coating of web-likematerial. The nozzle is made by machining in the closed tip of thetapered duct a transverse V-shaped groove at a machining angle in therange from 25 to 50°, such as 35 to 45°. The angle of the groove has animpact on the shape of the oval flow opening thus produced and hence onthe shape of the jet produced. The nozzle of the invention provides afairly rounded fan-shaped jet with soft edges, thus facilitatingoverlapping of adjacent jets so as to achieve optimally regular coating.

The flow duct is preferably circular in cross-section and straight.Before machining, the duct tip has preferably the shape of a sphericalsurface.

Enlargement of the V-shaped groove has proved to increase the wearresistance of the nozzle. In high-pressure spraying, flow rates are high(e.g. on the order of about 100 m/s), and coating compositions usuallycomprise solid substances (e.g. calcium carbonate), which substantiallyincrease the wear of nozzles.

The nozzle may comprise a preliminary nozzle. It acts as a preliminarydiffuser of the jet. The preliminary nozzle may especially comprise anexpanding flow channel. It is particularly useful for enhancing the wearresistance of the nozzle. In a number of embodiments, the flow channelof the preliminary nozzle may expand or taper in the flow direction.

The size (diameter of orifice) of the preliminary nozzle may be e.g. inthe range from 0.1 to 1 mm, typically in the range from 0.25 to 0.55 mm.The area of the preliminary nozzle orifice may account for e.g. at themost 50%, typically at the most 20% of the orifice area of the nozzleproper (secondary nozzle).

Also, a nozzle has now been invented, in which the ratio of the maximumdiameter to the minimum diameter of the oval orifice is markedly morethan 1, such as 1.2 to 3, especially 1.5 to 2.5. The nozzle orifice mayhave dimensions e.g. in the range from 1 to 0.3 mm×0.5 to 0.1 mm,typically 0.75 to 0.4 mm×0.35 to 0.15 mm.

Also, a nozzle has now been invented that comprises a secondary nozzle,a tapered flow duct and a preliminary nozzle connected in front of this,the area of the flow opening of the preliminary nozzle being at the most1.1 times the transverse area of the flow opening of the secondarynozzle. Optimally, the area of the flow opening of the preliminarynozzle is at the most equal to the transverse area of the flow openingof the secondary nozzle. Such a preliminary nozzle allows for increasedwear resistance of the preliminary nozzle.

The nozzles of the invention can be used in the coating of paper, suchas printing paper and cardboard, for instance.

Some embodiments of the invention are described in detail below. Theaccompanying drawings pertain to the written description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a nozzle of the invention and a preliminary nozzle to beconnected to the nozzle.

FIG. 2 shows the volume flow of the nozzle combination in FIG. 1 as afunction of time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The nozzle of FIG. 1 comprises a secondary nozzle 1 and a preliminarynozzle 2.

The secondary nozzle 1 has been manufactured by first making a piecehaving a straight tapered flow duct, which is circular in cross-sectionand comprises a closed tip shaped as a spherical surface. In the centerof the tip, a transverse V-shaped groove has been machined so as toprovide a nozzle orifice 3 with the desired transverse area. The nozzleorifice 3 is oval and it produces a fan-shaped jet.

The preliminary nozzle 2 comprises an expanding flow duct, whose feedorifice 4 is circular.

The grinding angle of the nozzle orifice 3 influences the shape of thenozzle orifice and the jet obtained with this. The smaller the grindingangle, the flatter the shape and the sharper the edge of the fan-shapedjet produced. The fan edges may further comprise forwardly orientedprofile peaks. An enlarged grinding angle will expand the oval shape ofthe flow cross-section, thus providing a jet profile which is rounderand better fitting with the profile of another jet.

In accordance with the invention, the grinding angle is in the rangefrom 25 to 50°, such as 35 to 45°. Accordingly, the ratio of the majoraxis to the minor axis in the oval orifice is in the range from 1.2 to3, such as 1.5 to 2.5. The fan angle of the jet thus produced is about90°. The angle between ground surface and the surface of the flow ductis preferably at least 90°, typically from 100 to 150°.

At a coating station, there may be nozzles aligned in one single row ate.g. 60 mm intervals at a distance of about 100 mm from the web. Thenozzles are preferably disposed overlapping at a suitable angle with aview to providing optimally regular double coverage.

It has also been found that the corner of the lower edge 5 of thegrinding side is most critical in terms of wear. This corner is roundedduring the wear of the nozzle, resulting both in a larger orifice areaand altered orifice geometry and consequently also in a different jetshape. The originally oval orifice will approach a rectangular shape.The larger the grinding angle, the lower the abrasion.

The impact of abrasion was studied with regard to a nozzle of FIG. 1 byspraying calcium carbonate paste (50% dry matter content) under apressure of 10 MPa. The volume flow (ml/s) as a function of time (h) isindicated in FIG. 2. The volume flow increases very strongly at theoutset. However, at the end of about 95 hours, the growing rate isdistinctly stabilized. At 336 hours, the preliminary nozzle wasreplaced, resulting in a 32% drop in the volume flow, which still was34% higher than the starting level. Subsequently, the abrasion curvewill be slightly gentler than that of two new nozzles. This ispresumably due to the fact that a new preliminary nozzle has a smallerorifice than that of a worn secondary nozzle. As a preliminary nozzlehas larger area of wear, the secondary nozzle will wear at a slowerrate. As the abrasion curve stabilizes, the sizes of the nozzle orificeareas approach each other. As the secondary nozzle was replaced at 670hours, the volume flow started to grow strongly again, thus supportingthe assumption above.

When a preliminary nozzle of one size category below was fitted in thenozzle, abrasion became markedly slower. Over two weeks (336 h), thevolume flow increased by 25% alone, and this can be readily compensatedfor with the aid of pumping pressure.

The area of the flow orifice of a preliminary nozzle should not be morethan 1.1 times the transverse area of the flow orifice of the secondarynozzle. The area of the flow orifice of the preliminary nozzle ispreferably at the most equal to the transverse area of the flow orificeof the secondary nozzle.

1-10. (canceled)
 11. An array of nozzles for use in coating byhigh-pressure spraying techniques a web of material moving in a firstdirection, the array of nozzles comprising: at least one row of aplurality of nozzles oriented transverse to the first direction; whereineach nozzle is comprised of a tapered duct ending in a closed tip inwhich a V-shaped groove has been machined, the V-shaped groove defininga nozzle orifice defining a transverse area, the nozzle orifice arrangedto form a jet of coating material; and wherein the V-shaped groove has afirst side and second side which intersect to define an angle which isbetween 25 to 50 degrees.
 12. The array of nozzles of claim 11, in whichthe angle is between 35 to 45 degrees.
 13. The array of nozzles of claim11, wherein each nozzle orifice transverse area is oval in shape. 14.The array of nozzles of claim 11, wherein the orifice defines a maximumdiameter and a minimum diameter and a ratio between said maximumdiameter and said minimum diameter which is greater than 1.2.
 15. Thearray of nozzles of claim 14, wherein the ratio is between 1.2 and 3.16. The array of nozzles of claim 15, wherein the ratio is between 1.5and 2.5.
 17. The array of nozzles of claim 11, wherein the nozzleorifice has dimensions of between 1.0-0.3 mm by between 0.5-0.1 mm. 18.The array of nozzles of claim 17, wherein the nozzle orifice hasdimensions of between 0.75-0.4 mm by between 0.35-0.15 mm.
 19. The arrayof nozzles of claim 11, wherein each nozzle comprises: a preliminarynozzle having portions forming a flow orifice, the flow orifice definingan area; a secondary nozzle having the nozzle orifice, the nozzleorifice arranged to form a jet of coating material, the secondary nozzlebeing connected to the preliminary nozzle; and wherein the preliminarynozzle is arranged to form a preliminary diffuser for the nozzleorifice.
 20. The array of nozzles of claim 19, wherein each preliminarynozzle comprises an expanding duct.
 21. The array of nozzles of claim19, wherein each preliminary nozzle flow orifice defines a flow orificearea which is at the most 1.1 times the transverse area of the nozzleorifice of the connected secondary nozzle.
 22. The array of nozzles ofclaim 21, wherein the flow orifice area of the preliminary nozzle is atmost equal to the transverse area of the nozzle orifice of the connectedsecondary nozzle.
 23. The array of nozzles of claim 19, wherein the floworifice of the preliminary nozzle has a diameter of between 0.1 mm and 1mm.
 24. The array of nozzles of claim 23, wherein the diameter of theflow orifice of the preliminary nozzle is between 0.25 and 0.55 mm. 25.The array of nozzles of claim 19, wherein the area of the flow orificeof the preliminary nozzle is equal to or less than 50 percent of thetransverse area of the nozzle orifice of the connected secondary nozzle.26. The array of nozzles of claim 25, wherein the area of the floworifice of each preliminary nozzle is equal to or less than 20 percentof the transverse area of the nozzle orifice of the connected secondarynozzle.
 27. The array of nozzles of claim 11 wherein the web of materialis a paper web.
 28. A method of coating a paper web by high-pressurespraying comprising the steps of: moving a paper web or cardboard web ina first direction past an array of a plurality of high-pressuresecondary spray nozzles which are arrayed transverse to the firstdirection; supplying each secondary spray nozzle of the array with aflow of coating by supplying coating at a pressure of 1 MPa to 200 Mpafirst to a preliminary nozzle then to the secondary spray nozzle, whichis connected to the preliminary nozzle; wherein the flow of coatingflows first through portions of the preliminary nozzle forming a floworifice, the flow orifice defining an area, then the flow of coatingflows through portions of the preliminary nozzle forming an expandingduct; thereafter the coating flows into a portion of the secondarynozzle forming a tapered duct ending in a tip which is closed but forportions of the secondary nozzle forming a transverse V-shaped groovehaving a first side and a second side which intersect to define an anglewhich is between 25 to 50 degrees, the V-shaped groove intersecting thetip to form a nozzle orifice defining a transverse area; and dischargingthe flow of coating through the nozzle orifice to form a jet of coatingmaterial directed at the paper web or cardboard web, wherein theexpanding duct of the preliminary nozzle forms a preliminary diffuserfor the flow orifice.
 29. The method of claim 28 wherein the nozzleorifice defines a maximum diameter and a minimum diameter and a ratiobetween said maximum diameter and said minimum diameter which is greaterthan 1.2.
 30. The method of claim 28 wherein the flow orifice area is atmost 1.1 times the transverse area of the nozzle orifice.
 31. The methodof claim 28 wherein the flow orifice of the preliminary nozzle has adiameter of between 0.1 mm and 1 mm.
 32. The array of nozzles of claim28 wherein the area of the flow orifice of the preliminary nozzle isequal to or less than 50 percent of the transverse area of the nozzleorifice of the secondary nozzle.
 33. An array of nozzles with reducedwear characteristics for use in coating by high-pressure sprayingtechniques a moving web of paper or cardboard mounted for motion in afirst direction, the array of nozzles comprising: at least one row of aplurality of secondary spray nozzles which are arrayed transverse to thefirst direction; wherein each secondary nozzle has portions defining atapered duct which ends with a tip which is closed but for portions ofthe nozzle forming a transverse V-shaped groove which intersects thetip, thereby defining a nozzle orifice defining a transverse area, thenozzle orifice arranged to form a jet of coating material; and whereinthe V-shaped groove has a first side and second side which intersect todefine an angle which is between 25 to 50 degrees, wherein eachsecondary nozzle is connected to a preliminary nozzle, so that thetapered duct ending with a tip is in flow receiving relation to portionsof the preliminary nozzle forming an expanding duct which in turn is inflow receiving relation to portions of the preliminary nozzle forming aflow orifice, the flow orifice defining an area, the flow orifice inflow receiving relation to a supply of coating at a pressure between 1MPa and 200 Mpa.
 34. The array of nozzles of claim 33, wherein thenozzle orifice defines a maximum diameter and a minimum diameter and aratio between said maximum diameter and said minimum diameter which isgreater than 1.2.
 35. The array of nozzles of claim 33 wherein thepreliminary nozzle flow orifice area is at the most 1.1 times thetransverse area of the nozzle orifice of the connected secondary nozzle.36. The array of nozzles of claim 33 wherein the flow orifice of thepreliminary nozzle has a diameter of between 0.1 mm and 1 mm.
 37. Thearray of nozzles of claim 33 wherein the area of the flow orifice of thepreliminary nozzle is equal to or less than 50 percent of the transversearea of the nozzle orifice of the connected secondary nozzle.
 38. Thearray of nozzles of claim 33 wherein the the preliminary nozzle has aflow orifice which is at the most 1.1 times the transverse area of thenozzle orifice of the connected secondary nozzle.